View Full Version : Cheap Chrono Build Log

02-07-2007, 12:27 AM
Figuring since I can get the most intelligent (and gramatically correct) input from this forum, I'm just going to base this project here.

The basic goal is to setup a cheap chrono you can build at home thats more accurate than the poor man's chrono (which I despise), that you can hook up to your computer via USB (so computer can handle calculations and data logging). This project can then be furthered externally for hook ups to PDAs, ipods etc for quick field testing where a laptop or computer isn't readily available.

Initial Steps:
1. We are going to initially do this entire setup using RS232 Serial ports, mainly because its easier and this way we can test how well the physical aspect works, we'll have to work towards USB later
2. Put together the physical aspect, The object is to make the chrono out of stuff you can find at radioshack and at home, and that hopefuly you don't need too many external tools.

Basic Design:
Coming Soon...

(This post is just a place holder for the moment, I'll write everything up in the next few days)

02-07-2007, 12:46 AM
I'm interested to see what you have in mind. I have always believed that the coke can chrono was unreliable and produced false results more times than not.

02-07-2007, 09:12 AM
I think you have a good idea, but I do have a question. Do you think you can design and build this for less then the cost of a real standalone chronograph? For example, I bought a brand new Chrony F1 chronograph a few months back for around $80 shipped. It's completely standalone, runs off a 9v battery, and will work with anything from airsoft guns to real steel rifles.

Don't let me discourage you from this project, but I wanted to make sure you knew things like this were out there.

02-07-2007, 09:34 AM
Furthermore, chronos can be commonly found on Ebay for even cheaper than buying through retailers.

02-07-2007, 09:49 AM
Yes I believe I can make it relatively cheaply, programming it is the main issue, and is the most time consuming. But programs are the most easy to replicate for free.

02-07-2007, 10:24 AM
Too bad Shooting Chrony doesn't sell refurb F1s anymore. They were around $38 shipped and in mint shape. Mishkan, I'm really interested to see what you come up with, especially the PC logging interface.

02-07-2007, 12:46 PM
I have always believed that the coke can chrono was unreliable and produced false results more times than not.

I agree, I did a poor mans chrono on a Pepsi can with a pellet rifle that I done some squirrel hunting with and according to this test my out of the box 850+fps pellet rifle barely penetrates the the bottom of the cans that I use. I find it odd that a hunting pellet rifle performs as poorly as my airsoft rifle. The only other thing I can think of for not being able to shoot through the cans is that the manufacturers are starting to make their cans thicker.

Please keep up informed on your project.

02-07-2007, 02:01 PM
Yes, not all cans are equal in thickness. The Coke can test should never be substituted for a real chrono.

02-09-2007, 05:04 PM
Physical Design (Disclaimer: Nothing in this should be taken as final design as this is mostly brainstorming and logging of the ideas and thoughts of the multiple people working on this)
So our first two possible ways of achieving our goal can possibly be done through optics. Initially optics seems the best possible solution due to inexpensiveness and the ease of setting an interrupt circuit using only a few components. Likely the most difficult component to find would be the Schmitt Trigger would allow for digital output of the sensor(s)

So to keep this simple there are two possible ways we thought of for achieving this initially and the problems that ensue with each.

1. Two sensors

This was the initial idea that we had it seems to be more accurate and reliable
Basically two sensors placed a fixed distance apart (could be used wth something as simple as nuts, washers, anything relatively precision machine made)
Just time the time between interrupts and use the distance to find the FPS (Under a ready state outputs one "blip" and then another)
Doesn't matter where the BB hits as long as it is consistent
Problem are involved such as alignment etc.

2.One Sensor

My friend proposed this idea to me actually earlier
This sensor could be achieved with just one, hypothetically if you know diameter of the BB then you can figure out the time that it interrupts the BB
You have to make sure that the BB hits it directly and centered
You have to know the exact diameter of the BB

We'll likely try both of these but I'm still leaning towards the two sensor design as we can't quite be sure how efficiently we can achieve either. Working on this we thinking it would be more reliable and easy to use than the single method, just construction is a tiny bit more complicated.

I'm currently in the process of talking with a few of the guys over at National Instruments about setting all this up. So far it looks like all of this is staying under $15 considering the chips cost less than a dollar. Researching all this might take a little bit more money and time.

02-11-2007, 04:04 AM
So here are the basic prices of everything electronic, not counting the wires or resistors (which I still have to figure out).
Based off Mouser prices
PIC chip 5.69
IR LED *2 = 0.32
Photodiode*2 = 1.44
Mini-b USB connector = .96 (can be changed out I just have a bunch of these type wires laying around or you can even just tear apart an existing wire)
IC Socket = .20 (optional just for putting in the PIC chip if you're unsure of your soldering)
Total = 8.61

Shipping on average is about 6 dollars so its about 15 in all for the electronic parts

Then the physical component can be pretty much anything as long you can align everything and maintain a constant distance between the two . We're working on a general design though at the moment

02-11-2007, 10:49 AM
Looking good but may I ask how much will you be paying for your hand held device? (Palm Pilot, Pocket P.C., Ipod, etc.)

02-11-2007, 05:38 PM
Well it doesn't matter what you use this is meant to act as a good alternative to the pricey chronos and crappy coke can. I'm not counting it in the price tag mainly because you'll be using it at home where there is likely to be a computer or if you use it at the field some person is bound to have an ipod. . The pic chip is capable of doing everything on its own I just don't feel like doing all the wiring as you probably understand.

02-12-2007, 05:35 PM
Everything is currently on order and the program is sort of in development. I'm setting up Labview for most of the data testing with some external plugins. The hardware sofar looks relatively simple to put together, you can use a solderless breadboard or it can easily be perfboarded considering there are very few physical components. I am buying different types of each of the products to help research into this.

02-13-2007, 08:06 AM
Always remember R&D can turn costly and ugly. But good luck to you and your project.

02-13-2007, 09:36 AM
Yeah I might end up asking for some small donations. All I can do now anyways is just sit around and wait.

02-17-2007, 07:25 AM
Anyhow after much deliberation I threw out the entire usb concept because I don't feel like this should depend on this programmer, plus programming the chips in general is a bitch. Anddd I've burnt out alot of infrared LEDs on the silly supply from the PC (albeit it is entertaining). So basically I rewrote the circuit for instead just a simple display of microseconds, then if you know the distance between sensors break out your calculator and do some easy math, here is the current diagram, the base light detection is very similar to unconventional's (why reinvent the wheel)


Now basically the jist of mine is it activates the timer til the second one turns it off (SR Latch by use of a 4001 chip) the chip should cycle at about 1 microsecond, this can easily be calibrated by using a pot and checking with a real chrono. Then this goes to a 3 digit counter, which is probably the most expensive piece other than the display, this then goes to the display buffer and then in turn to the 3 digit display.
(Tell me if you can't read it, I tried to adjust the contrast with curves to see how well it would help)

Overall the cost of the electronic parts is about
$14 not counting the board and wires
$7 Shipping probably

I'm really sorry to ask this, but can anyone donate money to help with this, ? (I'm ordering double parts to make sure I don't mess anything up so its quite a bit more expensive) My PayPal is Mishkan101@yahoo.com even if its $2 it'll help. I'll figure out some way to repay you, be it with my eternal gratitude or me putting together one of these for you).